1. Field of the Invention
This invention relates to soft-feeling coatings, and more particularly to waterborne soft-feeling coatings that contain surfactants and result in a lacquer-like finish with high gloss.
2. Brief Description of the Related Art
Soft-feeling paints and coatings provide desirable aesthetic and tactile characteristics for a variety of applications, particularly articles that are touched by consumers. Automotive manufacturers have used soft-feeling coatings on instrument panels, armrests, and horn buttons to give hard, glossy plastic components a velvety smooth matte finish. Other consumer products, such as notebook computers and cellular phones, also use soft-feeling coatings to enhance look and finish of the products and give the appearance of a high-quality product.
Typical soft-feeling coating compositions use a two-component (2K) solvent based paint. While this two-component coating has desirable features, the content of volatile organic compounds (VOCs) is high, on the order of 4.2 to 5.0 pounds per gallon. Increasingly stringent environmental regulations have forced coating manufacturers to use other solvent systems with lower levels of VOCs. In addition, two-component soft coatings often result in different gloss levels due to varying ambient humidity and different rates of solvent evaporation on different areas of the coated article. Due to these problems, some manufacturers have experienced difficulties in producing uniformly finished parts.
One component (1K) waterborne soft-feel coatings have been developed as an alternative to solvent-based coatings. These coatings have considerably less VOCs (on the order of 1.5 to 2 pounds per gallon). However, they are generally regarded as not as “soft” as the two-component solvent-based coatings. In addition, one component waterborne coatings exhibit poor chemical resistance and weatherability.
Recently, two-component waterborne soft-feel coating systems have been developed to overcome the shortcomings of the one-component system. A two-component waterborne system is described in a technical journal article by Ahmed (SAE Spec. Pub. SP-1135, pp 59-64 (1996)), and by Hegedus et al., J. Coat. Tech. 68, 51-61 (January 1996). However, such two component waterborne systems provide about one-half the level of gloss (measured as “distinction of image” or DOI) provided by the two component solvent-based system. Accordingly, such waterborne coatings are not suitable when a high gloss, soft feeling coating is desired. In addition, these coatings display inadequate wetting and flow characteristics when applied to substrates, which, in turn, result in surface defects. To combat these defects, additives such as flow modifiers are included to enhance the flow and level attributes of the composition.
Flow modifiers perform many functions in applied coatings such as paint. Flow modifiers are used primarily to reduce or eliminate surface defects, such as craters, fisheyes, pinholes, and orange peel. They also aid in pigment dispersion, help facilitate air release, improve substrate wetting, and promote flow and leveling. Although flow modifiers are typically used at 0.25-0.5% by weight in liquid coatings and at 0.5-1.5% by weight in powder coatings, based upon the weight of the coating, they can be effective at levels as low as in the parts per million (ppm) range.
Surfactant compositions have been disclosed for purposes such as cleaning compositions and rinse aids. For example, U.S. Pat. No. 4,989,621 to Pruehs et al. discloses the use of hydroxyalkyl polyethylene glycol ethers in rinse aid compositions for dishwashing machines. However, to the knowledge of the present inventors, such surfactants have not been disclosed for coating applications.
U.S. Pat. No. 4,925,587 to Schenker et al. discloses hydroxyalkyl polyethylene glycol and hydroxyalkyl polypropylene glycol ethers as foam inhibiting additives in low foam cleaning preparations. However, to the knowledge of the present inventors, such additives have not been disclosed for coating compositions.
U.S. Pat. No. 3,956,401 to Scardera et al. disclose low foaming, biodegradable nonionic surfactants of the formulaRO—(CH2—CHR′—O)x—(CH2—CH2—O)y—(CH2—CHR″—O)z                 where R is a linear alkyl hydrocarbon having an average from about 7 to 10 carbon atoms, R′ is a linear alkyl hydrocarbon of about 1 to 4 carbon atoms, R″ is a linear alkyl hydrocarbon of about 1 to about 4 carbon atoms, x is an integer from 1 to 6, y is an integer from 4 to 15, and z is an integer from 4 to 25. Such surfactants are liquid at room temperature, nongelling in aqueous solutions, and are useful as detergents. However, such surfactants have not been heretofore disclosed for coating compositions to the knowledge of the inventors.        
Amphoteric surfactants have been disclosed as a component of coating compositions. U.S. Pat. No. 5,399,617 to Farwaha et al. discloses amphoteric surfactants which are suitable as wet adhesion promoters and freeze-thaw stabilizers for use in both all acrylic and vinyl acrylic thermoplastic latex paints. However, the amphoteric nature of the surfactants makes them incompatible with certain solvents and undesirable for noncharged or positively charged surfaces.
Accordingly, there is still a need in the art for a waterborne, two-component coating composition that includes a surfactant to provide improved flow characteristics, soft-feel, and high gloss, as well as meet strict environmental guidelines. The present composition meets that need.